As discussed in my copending U.S. patent application Ser. No. 269,517, filed Nov. 10, 1988, the disclosure of which is incorporated herein by reference, exercise apparatuses or weight lifting machines have previously been developed whereby an exerciser who desires to develop certain body muscles employs such muscles to overcome resistance forces provided by the device. However, many prior art apparatuses provide only a constant resistance force during the exercise. It has been discovered that it is desirable to consider specific physical conditions of muscles during an exercise by varying the resistance encountered during the exercise motion. Unfortunately, the availability of exercise apparatuses capable of providing adjustable resistance patterns is limited at present.
For example, in what will be referred to as a "standard" weight lifting apparatus, there is provided a main support frame having upright members interconnected with crossmembers; a weight support carriage vertically movable within the main frame; a cable guide means fixed to the main frame; a length of cable secured at one end to the weight support carriage and reeved about the cable guide means; and a gripping means such as a handle which is secured to the free end of the cable for grasping by an exerciser to transmit force to vertically move the weight support carriage. As such, the resistance experienced by the user is the constant downward force of gravity on the weight support carriage. Thus, the resistance force is constant throughout the exercise movement and does not vary to achieve the benefits of maximum and minimum resistance at selected segments of the exercise cycle.
In an alternative embodiment of the "standard" exercise apparatus, the free end of the cable is attached to a cable wheel having a circular arcuate segment which is attached to a rotatable shaft supported on the main support frame. A bearing surface or surfaces, such as a leg extension pad, is also attached to the rotatable shaft by a bracket member in order that the user may apply force against the bearing surface to rotate the shaft and, hence, the cable wheel against the force of gravity which acts by means of the cable on the weight support member. As such, the resistance encountered by the exerciser in motivating the bearing surface is constant because the cable wheel arc segment is of a constant radius and the force thereby created by the weight support carriage applies a constant resistant torque thereto.
In an effort to provide a single variable resistance pattern in the last-described apparatus, Applicant believes that those in the art have replaced the circular cable wheel arc segment with a non-circular cam wheel which is rotatably mounted on the shaft and which has the cable attached thereto. As such, the cam wheel has a varying radius so that the moment arm formed at the point of tangency of the cable on the cam wheel varies during the exercise motion thereby varying the resistance. However, because the resistance is determined only by the shape of the cam wheel in such apparatus, in order to present alternative resistance patterns, the cable must be detached from the cam wheel, the cam wheel removed from the shaft and replaced by a replacement cam wheel, and the cable reattached to the replacement cam wheel. In addition to the time and effort required in changing cam wheels, a plurality of cam wheels is required to provide varying resistance patterns.
Apparently in an effort to provide varying effective cam surfaces which are connected to the weighted cable and which rotate on the rotatable shaft, the apparatus disclosed in U.S. Pat. No. 4,709,920 issued to Josef Schnell on Dec. 1, 1987 was developed. In that apparatus, the cable is attached between two spaced parallel disks having cooperating apertures therein. The user apparently places pins between the disks to define the cam surface between the disks which encounters the weighted cable. By varying the pin placement, the cam surface and, hence, the resistance pattern, may be varied. It is clear to those skilled in the art that such a system is fraught with serious practical shortcomings. First, the proper placement of the pins between the disks to generate a cam surface appears difficult for many users. Second, the time and effort in selecting and effecting pin placement is excessive. In addition, because the cable passes over a highly discontinuous surface defined by the pins, the smooth action required for effective and safe muscle development may be lacking.
The subject invention is directed toward an improved exercise apparatus allowing for readily variable resistance patterns which overcomes, among others, the above-discussed problems and provides an exercise apparatus presenting selectable effective cam surfaces connected to a cable coupled to a weight stack which allows for proper development or rehabilitation of an exerciser's musculature.